1. Field of the Invention
This invention is concerned with blood pressure measurement in which a determination of the systolic and diastolic blood pressure may be obtained by a method which is adaptable to automated apparatus.
2. Description of the Prior Art
The measurement of systolic and diastolic blood pressure commonly is carried out by a physician or nurse by the use of an inflatable cuff placed on the upper arm of the subject which is inflated to a pressure higher than the systolic blood pressure, causing an occlusion of the arterial vessels in the upper arm. The pressure in the cuff is then allowed to decline to a point less than the diastolic blood pressure which allows the unoccluded blood flow to resume. By use of a stethoscope the physician or nurse listening to the characteristic sounds (referred to as the "Korotkoff sounds") which have a characteristic transition associated with the systolic and diastolic pressures, the clinician may determine the cuff pressures at systolic and diastolic.
Due to the extremely widespread nature of the hypertensive condition, mass screening of the population for abnormal blood pressures has been recognized as a desirable objective, which mass screening would almost necessarily be carried out without the need for skilled physicians or nurses, i.e. the process would have to be automated. Numerous techniques for such automation have been proposed and implemented. Many of these involve the automated processing of data corresponding to the Korotkoff sounds in order to detect the systolic and diastolic pressures without the need for a skilled observer. These automated techniques relying on such Korotkoff sounds have certain disadvantages, one of which is the impracticality of its use in a relatively noisy environment.
This sensitivity to environmental noise usually has required the cuff to be placed about the upper arm of the subjects since these sounds are much attenuated and would not occur at a lower limb situs such as the wrist or finger. This placement on the upper arm requires partial disrobing of the subject and also is a relatively cumbersome procedure.
Other approaches to this objective have yielded techniques which can reliably detect systolic pressure, but in the case of detecting the diastolic pressure level, these techniques have produced rather poor results.
It is therefore the objective of the present invention to provide a method and arrangement for noninvasively determining the systolic and diastolic blood pressure which is readily adaptable to be automated while producing reliable results. It is another object of the present invention to provide such a technique which does not require the application of cuffs or other devices to the upper arm, but may be applied to the outer extremities, such as the index finger or wrist.